Generally, with reference to JP-2004-167658A, a reduction of a damage of a cutting tool having a chip evacuation groove is disclosed. In this case, the surface of the tip of the cutting tool is coated by a hard coating to restrict the damage of the cutting tool.
FIG. 5A shows a processed member 300 which has an opening portion 310 provided with a curved inner periphery surface (which surrounds an inner space). In this case, a first expected processed portion 321 and a second expected processed portion 322 are to be processed. A first hole (e.g., through hole) is to be formed at the first expected processed portion 321 to extend from an outer surface of the processed member 300 to reach the inner periphery surface of the processed member 300. A second hole or the like is to be formed at the second expected processed portion 322 and has an opening at the inner periphery surface of the opening portion 310. The first hole and the second hole are positioned corresponding to each other. The openings of the first hole and the second hole at the inner periphery surface face each other.
In the processing of the processed member 300, the cutting tool may break when the first expected processed portion 321 has been processed and then the second expected processed portion 322 is to be processed.
That is, the processing beginning surface (inner periphery surface of opening portion 310) of the second expected processed portion 322 is a curved surface, although the processing beginning surface (outer surface of the processed member 300) of the first expected processed portion 321 is a substantially flat surface.
In this case, as shown in FIG. 5B, the cutting tool 200 will flow (move) along the processing beginning surface of the second expected processed portion 322, in the case where the first expected processed portion 321 has been processed by the cutting tool 200 and the through hole 321a has been arranged and then the second expected processed portion 322 is to be processed. At this time, the upper portion of the cutting tool 200 is arranged in the through hole 321a. 
In this case, the chip evacuation groove is formed at the cutting tool, and positioned at the portion which is arranged in the through hole 321a. Thus, this portion is susceptive to breaking as compared with the case where the chip evacuation groove is not formed at this portion. Therefore, when the cutting tool 200 flows along the processing beginning surface (which is curved surface) of the second expected processed portion 322 in the state where the upper portion of the cutting tool 200 is arranged in the through hole 321a, the stress will be applied to the vicinity of the portion of the cutting tool 200 which is fixed to the through hole 321a. Thus, the cutting tool 200 will break.
Moreover, the following processing method is proposed in order to restrict the damage of the cutting tool 200. That is, as first, the first expected processed portion 321 is processed by the cutting tool 200. Thereafter, the processing beginning surface of the second expected processed portion 322 is flatted by other jig. Thereafter, the second expected processed portion 322 is processed by the cutting tool 200. However, in this case, if the processing beginning surface of the second expected processed portion 322 is flatted by the other jig, the processing time will increase. Thus, the cost will increase.